Steam admission valve structure for steam turbines

ABSTRACT

The valves are moved toward and from the seats by a valve lift bar provided with removable split bushing in which the valve stems are slidable. The stems are formed with enlarged integral head portions dimensioned to pass through the apertures in the bar in which the bushings are mounted. The heads are engaged by the bushings upon upward movement of the bar. Means is provided for proper vertical adjustment of the bushings in the bar to cause sequential movement of the valves form their seats upon upward movement of the lift bar.

United States Patent James Rodger Shields Pittsburgh, Pa. 867,017

Oct. 16, 1969 Dec. 7, 197 1 Carrier Corporation Syracuse, N.Y.

[ 72] Inventor [21 Appl. No. [22] Filed [45] Patented [73] Assignee [54]STEAM ADMISSION VALVE STRUCTURE FOR STEAM TURBINES 2 Claims, 4 DrawingFigs. [52] U.S. Cl l37/630J9, 137/501, 251/77 [51] lnt.Cl Fl6k l/00,F16k 31/44 [50] Field of Search ..137/630.16, 630.19, 635; 251/77; 308/4R, 5 V [56] References Cited UNITED STATES PATENTS 2,385,537 9/1945Pentheny... 137/630. 19

2,790,453 4/1957 Maloney 251/77 X 2,830,620 4/1958 Shuptrine 137/630. 19

2,777,466 H1957 Ericson l37/630.l9 FOREIGN PATENTS 505,425 8/1930Germany 308/4 Primary E.raminer Robert G. Nilson Attorneys-Harry G.Martin, Jr. and .1. Raymond Curtin ABSTRACT: The valves are moved towardand from the seats by a valve lift bar provided with removable splitbushing in which the valve stems are slidable. The stems are formed withenlarged integral head portions dimensioned to pass through theapertures in the bar in which the bushings are mounted, The heads areengaged by the bushings upon upward movement of the bar. Means isprovided for proper vertical adjustment of the bushings in the bar tocause sequential movement of the valves form their seats upon upwardmovement of the lift bar.

PATENTED DEC 7 I97! SHEET 1 [IF 2 INVENTOR. J. RODGER SHIE) 05 BYATTORNEY PATENTEDDEC nan SHEET 2 [IF 2 BACKGROUND OF THE INVENTIONDifferent valve arrangements are used to control the admission of steaminto steam turbines. In one arrangement, the bottom wall of the steamchest is formed with a plurality of steam passages. A precision machinedseat is mounted in each passage. A valve is movable vertically into andout of engagement with each seat to control the admission of steam fromthe steam chest through the passages, each of which is connected to agroup of first stage nozzles.

As the demand load on the turbine increases, the valves are movedupwardly from their seats in a predetermined sequential order by a valvelift bar which is mounted above the series of seats for movement towardand from the same. The lift bar is formed with an aperture verticallyaligned with each valve seat. Each valve has a stem that extendsupwardly through an aperture and is slidable in the aperture. The upperend portions of the valve stems are threaded to receive stop nuts. Whenthe lift bar is moved upwardly, it engages the stop nuts on the valvestems, and moves the valves upwardly from the seats. The sequence inwhich the valves are moved from their seats and the extent of suchmovement is determined by the position of the stop nut on each valvestem, and jam nuts are provided to lock the stop nuts in adjustedposition.

The lift valve is reciprocated vertically by a servomotor which iscontrolled by a governor, whereby the valves are opened and closedsequentially according to the load demand on the turbine. Thesequential, rather than simultaneous, operation is employed-to providefor the admission of steam to select groups of nozzles in apredetermined order for more efficient turbine operation and for betterbalance with minimum vibration. Accordingly, upon initial upwardmovement of the lift bar, a valve having stop nuts adjusted close to thelift bar will be first moved to open position. The valve of the serieshaving the stop nuts on its stem adjusted to a higher position will openupon further upward movement of the lift bar, and so on. With the liftbar in its uppermost position, all of the valves are open, and as thelift bar is moved downwardly, the valves are closed in reversesequential order.

Due to the high velocity of the steam, and turbulence thereof in thesteam chest, vibration of substantial magnitude is set up and isimparted to the valve gear. The threaded end portions of the valve stemscreate areas where fatigue failure develops, which on occasion resultsin fracture of the valve stem. Such an occurrence creates a seriousproblem. Obviously, a valve with a broken stem is inoperable and thespeed and performance of the turbine can no longer be controlled withaccuracy, and in some cases not at all. Also, there is the great dangerthat the broken end of a stem, and/or the stem nuts, may pass throughthe valve seat and through the nozzles and be ingested in the blades ofthe turbine rotor, necessitating an expensive repair job.

This invention has as an object a steam admission valve arrangement ofthe lift bar type, embodying a structural arrangement by which fatiguefailure is reduced to a minimum, if not entirely eliminated, and thedanger of components of the valve gear being ingested in the turbine issubstantially eliminated.

SUMMARY OF THE INVENTION The steam admission valves are lifted fromtheir seats by a valve lift bar provided with removable split bushingsthrough which the valve stems extend. The upper ends of the stems haveenlarged integral heads dimensioned to pass through the apertures in thelift bar in which the bushings are mounted, but are engaged by thebushings when the bar is moved upwardly. Each bushing is formed at itsupper end with a radial flange. The bushings are adjusted vertically bythe use of annular shims placed between the flange of the bushing andthe bottom of the counterbore in the aperture in the lift bar.

2 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of theupper portion of a turbine steam chest including a valve structureembodying my invention, the lift bar and valves being shown inelevation;

FIG. 2 is an enlarged sectional view of the left end portion of thestructure shown in FIG. 1;

FIG. 3 is a sectional view of the lift bar, a pair of valves, and valveseats, the valve stems being provided with conventional adjusting nuts;and

FIG. 4 is an enlarged sectional view illustrating a modified form ofbushing.

DESCRIPTION OF THE PREFERRED EMBODIMENT I0 designates a steam chesthaving a steam inlet 11 and a bottom wall 12. The chest is provided witha cover 13 formed with upwardly extending brackets 14 in which there isjournaled a valve-actuating shaft 15.

The cover is also formed with hubs l7 apertured to slidably receive liftbar actuating rods 20, the upper ends of which are pivotally connectedto arms 23 fixed to the shaft 15, the connection being by way of clevis25.

The bottom wall I2 of the steam chest is formed with a linear series ofpassages in each of which there is mounted a valve seat 27. Valve liftbar 30 is attached to the actuating rods 20 and is arranged above thevalve seats 27. The lift bar is formed with an aperture in verticalalignment with each valve seat 27.

A split bushing 33 is positioned in each aperture in the lift bar 30.The upper portions of the apertures in the lift bar are counterbored orotherwise enlarged to form shoulders 35 spaced downwardly from the topside of the bar. Each bushing 33 is formed with a radially extendingflange 40 spaced upwardly from the lower end of the bushing.

The valves 41 are formed with stems 42. The upper ends of the stems areformed with integral enlarged heads 43 which are dimensioned forinsertion through the apertures in the bar 30. With the valve stemsinserted through the apertures in the lift bar, the split bushings arepositioned about the valve stems 42 and are moved downwardly into theapertures with the flanges 40 engaging the shoulders 35.

The bushings 33 are retained against upward vertical displacement fromthe bar 30 by retaining means. In the arrangement disclosed, thecounterbores are formed adjacent their upper ends with circumferentiallyextending grooves for the reception of snaprings 47 which extendinwardly over the flanges 40. However, it will be apparent that otherforms of retaining means may be used.

The lift bar 30 is moved upwardly upon oscillation of the shaft 15 whichis brought about by operation of a servomotor under the control of theturbine governor. This motor effects vertical movement of the length 50,the upper end of which is connected to an arm 51 fixed to the shaft 15.As previously stated, the valves 41 are moved upwardly from the seats 27successively in a predetermined sequence. For example, the numbersappearing below the valves in FIG. 1 illustrate one sequentialoperation, the valve at the center of the series being the first toopen, and the adjacent valve to the left being the second to open in theseries, and so on as indicated by the numerals 1 to 7.

Preferably, the operation is such that the second valve to be openeddoes not begin to open until the steam ring pressure on the nozzle orgroup of nozzles supplied by the first valve has built up to a pointslightly below throttle pressure. Similarly, each succeeding valve doesnot begin to open until the ring pressure on the preceding nozzle grouphas built up to approximately throttle pressure. The pressureestablished by the operation of each valve is determined in part by theposition of the lift bar 30 as each bar is engaged. In other words, itdepends on how far the lift bar travels upwardly after it has engagedand started to move a valve. It is therefore necessary that the lift barsuccessively engages the valves in accordance with the selected sequenceand at a relatively precise position of the bar.

In the arrangement of my invention, the enlarged head portions 43 of thevalves are engaged by the bushings 33. in order to effect engagement ofeach valve head 43 at the proper instant, means is provided foradjusting the bushings 33 axially in the bar 30. The distance betweenthe shoulders 35 and the retaining rings 47 is substantially greaterthan the axial dimension of the flanges 40. Accordingly, spacing shims53 are positioned between the shoulders 35 and the flanges 40 and/orbetween the flanges 40 and the retaining rings 47. With thisarrangement, the bushings 33 are adjusted axially in the bar 30 over alarge range commensurate with the difference between the thickness ofthe flanges 40 and the spacing of the shoulders 35 and retaining rings47.

As illustrated in FIG. 4, the bushings 33 may be dimensioned to extend aconsiderable distance upwardly from the flanges 40. With thisarrangement, different lengths of bushings can be employed, permittingthe valves 41 to be of like dimension. in other words, by making thebushings of different axial length, it is not necessary to make thevalve stems of difierent axial length.

The construction presently employed is illustrated in FIG. 3 wherein theupper ends of the valve stems are threaded to receive adjusting nuts 60.These nuts are adjusted axially on the valve stems to provide for properengagement of the lift bar 30 with each valve to effect opening of thevalves in the proper sequence. As previously stated, vibration impartedinto the valve stems during operation of the turbine develops fatigue inthe threaded end portions of the valve stems and, on occasion, the stemsfracture.

it will be apparent that with my invention, the likelihood of fatiguefailure occurring in a valve stem has been reduced to a minimum, and,also, the hazard of components of the structure being ingested in theturbine has been eliminated.

lclaim:

l. A steam admission valve structure for steam turbines comprising afixed member formed with plurality of passages disposed vertically andarranged in side-by-side relation, each of said passages being providedat its upper end with a valve seat, a one piece valve lift bar mountedabove said seats for movement toward and from the same, said bar beingformed with an aperture axially aligned with each of said valve seats, asplit bushing mounted in each of said apertures, retaining meansdetachably mounted in each of said apertures for fixing each of saidbushings against axial movement relative to said bar, a valve cooperablewith each of said seats, each of said valves having a stem extendingthrough one of said bushings and being slidable therein, each of saidvalve stems being formed with an integral enlarged head portion, andsaid head portions being dimensioned for passage through said aperturesand engageable by the bushings upon upward movement of said lift bar,each of said apertures being formed with a shoulder spaced downwardlyfrom said retaining means, each of said bushings being formed with aradially extending flange positioned intermediate to said shoulder andsaid retaining means, said retaining means being positioned upwardlyfrom said shoulders a distance exceeding the axial thickness of saidflanges, a plurality of annular shim members encircling each of saidbushings, said shims in conjunction with said flanges filling the spacesbetween said shoulders and said retaining means and means operable toeffect vertical reciprocation of said lift bar to move said valves intoand out of engagement with said seats.

2. A valve structure as set forth in claim I, wherein said retainingmeans consist of a snapring positioned in each of said aperturesupwardly from said shoulders.

1. A steam admission valve structure for steam turbines comprising afixed member formed with a plurality of passages disposed vertically andarranged in side-by-side relation, each of said passages being providedat its upper end with a valve seat, a one piece valve lift bar mountedabove said seats for movement toward and from the same, said bar beingformed with an aperture axially aligned with each of said valve seats, asplit bushing mounted in each of said apertures, retaining meansdetachably mounted in each of said apertures for fixing each of saidbushings against axial movement relative to said bar, a valve cooperablewith each of said seats, each of said valves having a stem extendingthrough one of said bushings and being slidable therein, each of saidvalve stems being formed with an integral enlarged head portion, andsaid head portions being dimensioned for passage through said aperturesand engageable by the bushings upon upward movement of said lift bar,each of said apertures being formed with a shoulder spaced downwardlyfrom said retaining means, each of said bushings being formed with aradially extending flange positioned intermediate to said shoulder andsaid retaining means, said retaining means being positioned upwardlyfrom said shoulders a distance exceeding the axial thickness of saidflanges, a plurality of annular shim members encircling each of saidbushings, said shims in conjunction with said flanges filling the spacesbetween said shoulders and said retaining means and means operable toeffect vertical reciprocation of said lift bar to move said valves intoand out of engagement with said seats.
 2. A valve structure as set forthin claim 1, wherein said retaining means consist of a snapringpositioned in each of said apertures upwardly from said shoulders.